Operation of sodium batteries [e.g., ZEBRA batteries and sodium-sulfur (Na/S) batteries] at intermediate temperatures 200° C.) has several advantages, including lower degradation in cell performance and ability to use low cost materials for construction and sealing. However, it is a well-known problem in the technical art that molten sodium does not adhere (i.e., wet) well at intermediate temperatures to the solid electrolyte in sodium batteries. Poor wettability can lead to pooling of molten sodium in a localized area (i.e., “localization”) at the base, e.g., on the anode side of the solid electrolyte. Localization of sodium metal reduces the active area of the cathode. “Active area” (or “effective operation area) as defined herein is the fraction (or portion) of the cathode actively engaged in transfer of ion charge through the solid electrolyte to the anode or vice versa. The active area of the cathode varies depending on the area amount of the solid electrolyte in direct physical contact and in operation with sodium formation in concert with the anode. Reduction in active area decreases the capacity to transfer ion current through the solid electrolyte during operation, which decreases the effective efficiency and energy capacity of the battery (cell) upon demand. Decrease in cell performance can be particularly pronounced at intermediate temperatures 200° C.) when wetting of the electrolyte surface by sodium is reduced.
Accordingly, new devices and processes are needed that expand the active area of the cathode during operation that increases the energy cycling and charge transfer capacity of sodium batteries. The present invention addresses these needs.